Less than a week after sounding confident about the NCAA's capacity to slow down uptempo offenses, Air Force head coach and NCAA Football Rules Committee chairman Troy Calhoun has seemingly had a change of heart.

According to David Ching of ESPN.com, Calhoun said rule changes would only occur if there was decisive proof that playing at a higher tempo increased the risk of player injury:

The key is this: I think the only way that it can or it should become a rule is if it is indeed a safety concern. And that can't be something that's a speculation or a possibility. I think there's got to be something empirical there where you realize, "Yep, this truly is a health matter" in terms of not being able to get a defensive player off the field.

This about-face comes six days after Calhoun's assertion that a change would be made "to enhance student-athlete safety by guaranteeing a small window for both teams to substitute," according to Ching.

In the interim, coaches throughout the nation have weighed in on the issue of slowing down uptempo offenses—even more than they had before. Prior to Calhoun's comments, this was already a complex and hot-button issue.

Now it's on fire.

One of if not the single most outspoken persons on this matter has been Auburn head coach Gus Malzahn, who, as an adherent of the uptempo offense, has a vested stake in keeping it alive and in its current form.

Per Ching, Malzahn said to reporters on Tuesday, "There's absolutely zero documented evidence that is hazardous on the pace of play, only opinions."

If hard evidence is indeed what's needed to outlaw uptempo offenses from college football, the rules committee will need to obtain some quickly.

Given Calhoun's most recent comments, it appears the committee is not in possession of any such tangible evidence to prove uptempo offense causes injuries. And in order to go into effect next season, the rule would need to be passed by the Playing Rules Oversight panel when it convenes on March 6.

Some of the changes Calhoun and the committee have discussed include adding an extra timeout, among several other things.

This offseason was dedicated as one where the only rule changes made would concern player safety, and to some people—Arkansas' Bret Bielema and Alabama's Nick Saban, for example—conventional logic dictates that uptempo offenses put players at risk.

But until that logic turns into cold, hard facts, Calhoun and the rest of the committee will be forced to keep the rule as is.